The present invention relates to a rubber granulating machine and method, and more particularly to a process and apparatus for grinding rubber or similar material. The rubber or similar material is ground into a usable or marketable end product such as rubber powder that may be used in the rubber industry.
The disposal or reuse of previously used rubber products, such as rubber tires, presents many problems. Ecologically, rubber tires degrade very slowly and if disposed of improperly, may lead to hazardous environmental conditions in terms of both potential ground water problems and other ecological effects. Recently, recycling of pre-used rubber products has increased in popularity in order to avoid potential negative environmental impact as well as to provide potentially commercially reusable rubber products.
Several methods for recycling used rubber products exist. Often, rubber products such as rubber tires are rendered into dust or fine particulate rubber which then may be reused in other rubber products. However, one of the difficulties with recycling rubber products such as tires is that such products are extremely durable and consequently difficult to reduce to a re-usable form. In order for any recycling effort to be cost effective, a method must be developed to reduce the extremely durable rubber products to a form of rubber that may be useable in further generating processes. Recycled rubber particles become more commercially valuable with decreasing particle size. The commercial value increases because rubber particles of smaller sizes may be more easily incorporated into a wider variety of new rubber products.
U.S. Pat. No. 4,813,614 issued to Moore et al. entitled, “Method and Apparatus for Treating Waste Products to Recover the Components Thereof” illustrates an early method for recovering rubber particles from pre-used rubber products such as tires. In Moore, used products such as used rubber tires are frozen using liquid nitrogen and are then crushed. The particles are re-frozen and re-crushed in successive stages to yield finer and finer rubber particles. The crushed output is then separated with regard to the size of the crushed particles and crushed particles may then be sold and/or reused based upon their size. In order to lower the temperature of the rubber tires sufficiently so that the rubber tires behave more solidly and less elastically so that the rubber tires may be crushed, Moore relies on a large quantity of liquid nitrogen. Liquid nitrogen is, of course, expensive to use. Thus, although the Moore process may yield fine particulate rubber, it is quite expensive.
U.S. Pat. No. 5,695,131 issued to Wenzel entitled “Shredder Separator” illustrates another device for recycling used rubber products such as rubber tires. The shredder separator of Wenzel includes a number of rotating blades that cut or shred a tire into small pieces. The shredding separator of Wenzel operates at ambient (i.e., generally room temperature) and thus avoids the expensive liquid nitrogen cooling steps of Moore. However, the product output by Wenzel's shredder is undoubtedly inferior to the product output by Moore for use in new rubber products because of the larger output size of the rubber particles. Because the shredder relies on a number of rotating blades rather than successive crushing steps, the recycled rubber particles are far larger than the rubber particles of Moore and consequently less commercially desirable for many applications. While large size particles may be suitable to such applications such as playground flooring and the like, the output of Wenzel is less suitable for reconstitution into new rubber products. By comparison, the fine rubber particles of Moore may be considerably more easily and economically incorporated into new rubber products.
U.S. Pat. No. 5,299,744 to Garmater entitled “Granulating Separating and Classifying Rubber Tire Materials” illustrates a further system for recycling used rubber tires. As with Wenzel, Garmater includes a rotating cutter wheel for reducing large chunks of tire into smaller chunks which may be reusable for some purpose such as ground cover for playgrounds, jogging trails, and the like. As with Wenzel, the rubber particles produced by Garmater are fairly large and maybe suitable for ground cover applications rather than applications such as reconstitution into new rubber products.
Thus, rubber recycling reclamation or granulating machines may be classified into two types. A first type produces fairly large rubber particles and operates at room temperature, often using rotating knives or knives of some sort to produce the particles. The process is fairly inexpensive. However, the large rubber particles produced, while usable for applications such as ground cover, are not generally usable for more commercially desirable applications such as new rubber products. A second type of rubber reclamation is the type shown in Moore in which the machinery operates at extremely lower temperatures and produces fine particles. Because the process operates at low temperatures, the process is fairly expensive. The rubber particles produced, however, may be employed in new rubber products.
Additionally, although the processes of Wenzel and Garmater may produce some small amount of fine particles, for example as a byproduct of the process, such particles are a very small fraction by weight of the output of the process. Only a small fraction of the total rubber material processed using the processes of Wenzel or Garamater may yield fine particle sizes.
Thus, a need exists for an improved method and apparatus for reducing rubber products such as pre-used rubber products, into fine grain particles with a high process efficiency. A need has especially existed for such a method and apparatus able to operate with lower cost.
It is therefore an object of the present invention to minimize the expense of producing commercially reusable rubber particles by providing a cost-effective, generally ambient temperature process that eliminates costly liquid nitrogen freezing.